This application claims the right of priority of German patent application No. 199 55 860.4 filed Nov. 20, 1999, the disclosure of which is incorporated herein by reference.
The invention relates to an axial face seal, in particular a running gear seal, having an angular sliding ring and a circumferential surface designed to accommodate a ring-shaped sealing member. The sealing member comprises a secondary seal in the area of the sealing leg of the sliding ring.
U.S. Pat. No. 4,256,315 discloses an axial face seal of this type. In order to prevent dirt from entering the sliding surface area, the ring-shaped sealing member is provided with a secondary seal in the form of a sealing lip that is molded onto the sealing member, so as to form one piece. To be sure, this prevents dirt from entering the area between the back of the sliding ring and the sealing member, but causes problems with the pre-assembly and the final assembly of the seal, particularly with respect to the secondary seal, which has a material cross section that is designed to be considerably thinner than that of the sealing member itself. As a result of material fatigue of the sealing lip, it can therefore happen during operation that the internal stress provided for in the area of contact with the sealing leg may no longer be sufficient to ensure that dirt does not penetrate.
To correct this problem, German Patent Document No. C 197 53 918 discloses an axial face seal, for which the secondary seal is made of an inherently stable, pressure-resistant material that is designed as separate component, is connected to the sealing member and supports itself axially on the sealing leg. The sealing lip of the secondary seal can be pressed against the outside circumferential surface of the sealing leg with the aid of an element that is elastic in radial direction.
The use of an inherently stable, pressure-resistant material now permits reduced tolerances for the seat in the machine housing, so that a more secure seating is possible. However, the area where the sealing lip rests on the outside circumference of the sealing leg is still considered to be problematic. Owing to the spherical design of the outside circumferential surface of the sliding ring, it can happen that during the assembly of the sliding ring, the sealing lip of the secondary seal comes to rest against the smaller dimensioned lower region of the spherical circumferential surface. As a result, the spring force that is directed toward the inside is no longer sufficient to efficiently prevent dirt from entering.
It is an object of the invention to provide an axial face seal, so that in addition to a more precise transfer of rotational moments from the sealing member to the sliding ring, the sealing effect in the region between the secondary seal and sliding ring is increased. The increased sealing effect is the result of improved cooperation between sealing member, secondary seal and sliding ring.
This object and others to become apparent as the application progresses, are achieved according to the invention in that the sealing leg of the sliding ring has a ring back with an axial projection extending in the direction of the sealing member. The secondary seal in the unassembled state is designed to be at a radial distance to the sealing leg or the projection and has at least in part a larger diameter than the sealing member. At least a free end of the secondary seal can be positioned with radial compression against the sealing leg or the projection by a component that holds the sealing member.
At least the free end of the secondary seal can be provided with a larger outside diameter than the remaining region of the sealing member to effect the aforementioned radial compression in the assembled state. For example, the free end of the secondary seal may expand outward in a conical shape, starting with the area where it is connected to the sealing member.
In the unassembled state of the axial face seal, the secondary seal does not come in contact with the outside circumference of the sealing leg or its axially extended projection. The secondary seal is reduced to the outside diameter of the sealing member only after the sealing member has been pressed into a respective bore for holding it. The secondary seal then comes to rest with radial compression so that it is forced against the corresponding circumferential surface of the sealing leg or the projection.
To optimize the sealing effect in this region, it is suggested that sealing lips be formed on the secondary seal profile facing the outer circumferential surface of the sealing leg, which sealing lips may form gaps.
In the pre-assembled or partially assembled state of the sliding ring, grease may be inserted as an anti-grinding agent into a hollow space between sealing member, secondary seal and the region on the back of the sliding ring. The grease can be inserted via the gap that still exists between the secondary seal and the outside circumference of the sealing leg or its axial extension. However, adding the grease is not required.
To achieve an optimum twisting safety between the sliding ring and the sealing member, depressions can be provided on the ring back, if necessary distributed evenly over the circumference, which are preferably molded into the sealing leg of the sliding ring. Ridges that extend approximately in the axial direction are formed onto the sealing member and can subsequently engage in these depressions. They can thus serve as a twisting safety to prevent the sliding ring from slipping, relative to the sealing member, as a result of high rotational moments and the grease if inserted.